For those unfamiliar with buying a gun in the US, you have to fill out ATF form 4473 which asks a BUNCH of disqualifying questions. This is what tripped up Hunter Biden (line 21g).

21a) Are you the actual transferee/buyer of all of the firearm(s) listed on this form and any continuation sheet(s) (ATF Form 5300.9A)? Warning: You are not the actual transferee/buyer if you are acquiring any of the firearm(s) on behalf of another person. If you are not the actual transferee/buyer, the licensee cannot transfer any of the firearm(s) to you. Exception: If you are only picking up a repaired firearm(s) for another person, you are not required to answer 21.a. and may proceed to question 21.b.

21b) Do you intend to purchase or acquire any firearm listed on this form and any continuation sheet(s), or ammunition, for sale or other disposition to any person described in questions 21©-(m), or to a person described in question 21.n.1 who does not fall within a nonimmigrant alien exception?

21c) Do you intend to sell or otherwise dispose of any firearm listed on this form and any continuation sheet(s) or ammunition in furtherance of any felony or other offense punishable by imprisonment for a term of more than one year, a Federal crime of terrorism, or a drug trafficking offense?

21d) Are you under indictment or information in any court for a felony, or any other crime for which the judge could imprison you for more than one year, or are you a current member of the military who has been charged with violation(s) of the Uniform Code of Military Justice and whose charge(s) have been referred to a general court-martial?

21e) Have you ever been convicted in any court, including a military court, of a felony, or any other crime for which the judge could have imprisoned you for more than one year, even if you received a shorter sentence including probation?

21f) Are you a fugitive from justice?

21g) Are you an unlawful user of, or addicted to, marijuana or any depressant, stimulant, narcotic drug, or any other controlled substance? Warning: The use or possession of marijuana remains unlawful under Federal law regardless of whether it has been legalized or decriminalized for medicinal or recreational purposes in the state where you reside.

21h) Have you ever been adjudicated as a mental defective OR have you ever been committed to a mental institution?

21i) Have you ever been discharged from the Armed Forces under dishonorable conditions?

21j) Are you subject to a court order, including a Military Protection Order issued by a military judge or magistrate, restraining you from harassing, stalking, or threatening your child or an intimate partner or child of such partner?

21k) Have you ever been convicted in any court of a misdemeanor crime of domestic violence, or are you or have you ever been a member of the military and been convicted of a crime that included, as an element, the use of force against a person as identified in the instructions?

21l) Have you ever renounced your United States citizenship?

21m) Are you an alien illegally or unlawfully in the United States?

21.n.1) Are you an alien who has been admitted to the United States under a nonimmigrant visa?

21.n.2) If you are such an alien do you fall within any of the exceptions stated in the instructions? (U.S. citizens/nationals leave 21.n.l and 21.n.2 blank)